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MAF ground, cycling?


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52 replies to this topic

#26 Cougar

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Posted 19 December 2012 - 10:38 AM

Well it sounds like you are making progess since you found the loose rotor. I still have to wonder about the hissing injector. It sounds like air may be getting by the seal for injector. Have you checked for that?

#27 86 Wonder Wedge

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Posted 19 December 2012 - 11:26 AM

The injector, I believe, is original. I have replaced the seals/gaskets when I had the throttle body apart (if it sounded otherwise, my apologies). And as far as I look, 24 @ idle and a 20psi hold pressure are dead on for factory specs.

And the hissing sounds more like when you spray a spray bottle (that "pffft" sound when you squeeze the trigger) at random times and a really short interval, like the ECU has an extra long pulse in there or the pintle moves farther away for a split second...

And no, I haven't torn apart the throttle body yet to check for defects/missing/damaged parts....

#28 ivans imports

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Posted 19 December 2012 - 11:32 AM

had one that a guy put coalman camp feul in hiss loyale made the injector stick randomly and fail stuck wide open [ was a pain to fix ] could the injector be sticking ? also have you verifyd the timing a pop out the intake indacates retarded timing.

#29 86 Wonder Wedge

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Posted 19 December 2012 - 11:52 AM

Timing is verified 20 BTDC on #1 (front pass side cyl) with the green connectors plugged in.

And could be possible, but I run periodic SeaFoam through it and constant Shell gasoline (it's the only Top Tier fuel supplier in the area) and the fuel/induction system is SPOTLESS. No fuel staining, no oil residue, the throttle plate is still mirror-gold colored and the injector housing gaskets around the outside are dry as a bone.

Resistance of the injector tests out at 1.2 ohms. I little on the high end, but still within the 0.5>2 ohm range...

#30 Cougar

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Posted 19 December 2012 - 09:40 PM

See if cleaning the engine and chassis grounds makes any improvement. Use a fine wire brush and wipe them clean with a cloth.

#31 86 Wonder Wedge

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Posted 24 December 2012 - 05:46 PM

UPDATE. So it finally got "seasonably" cold today (near 26F or so..) and the car spit-up a code 24 (IAC code), it would idle at 400/500 RPM until warm, but still idles worse, I power off, power on, start and then the CEL disappears and idles like it has been. And the code has been intermittent in the last couple days.. happens more when it sits overnight/dead cold.

Also, (newer symptom) but in 2nd gear and beyond, I WOT it and above 5K, it will just hit a wall around 5250 to 5400 RPM (varies) and I keep WOT it, it will bog like fuel cut for a rev limiter, then 1-2 sec later, it will kick back, hard and feel like I hit a nitrous shot...

Haven't been able to go out and inspect the bundle connections, but the grounds are super clean, but I'm going to "temporarly" add another ground from the motor to the body to see if it makes a difference...

#32 Cougar

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Posted 24 December 2012 - 08:26 PM

The info I looked at shows that code 24 is for 'Air control valve or circuit', for a 88 or later model. The trouble could be electrical.

Edited by Cougar, 24 December 2012 - 08:43 PM.


#33 86 Wonder Wedge

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Posted 26 December 2012 - 10:02 PM

More updates:

Driving around now, the code 24 is constant when cold and does not clear until operating temp and a system restart.

NEW SYMPTOM: It will not rev over 5250 RPM with WOT. In any gear, from any specific speed UNLESS I back off to 75-90% throttle. And it loses MAJOR power from 3K on....

Also dropped in a new CAS (OEM Hitachi. :drunk: ) with zero change. The connectors are all clean and clear, the ground resistance between motor and body, body and battery and motor and battery at 0.03K Ohm. Near zero. All the bundle connectors are spotless, wiring is all in it's original loom and wires, and the alt has 0.03 mVAC output (negligible, thinking it was screwing up the ECM).

Also checked the injector to check for split orings or a missing isolator (to account for the loudness) and both were like new when I put them in 5 months ago and assembled correctly according to the FSM...

However, I cleared the codes approx 1-2 weeks ago and ran the D-Check mode again today and came up with codes 11, 13, 23, 24 and 31. What the what? And the only code that pops with the CEL on (when cold) is the code 24.

Now I'm throughly lost...

#34 Cougar

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Posted 26 December 2012 - 11:05 PM

Check to see if you have 12 volts getting to the IAC valve. You may have to replace the valve. I would suspect the other codes are being caused by a common power link problem to the sensors.

#35 86 Wonder Wedge

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Posted 28 December 2012 - 02:37 PM

Yep, getting 11.76 (BAT voltage) at the plug and a resistance of 10.6 across the IAC plug, but does not "cycle" after 1 min like the FSM says it should. I've also hooked the IAC to a 12V source and cycled it manually and it still open/closes.. I tried testing the voltage at the ECU per the FSM, but the FSM I'm using is the MY89.

I've read that the MY91 and MY89 SPFI are identical, but after 2 min, I wasn't getting voltage but can't rule out the computer since the wire colors didn't match (even though the ECU plugs had the same number of wires and connectors)

The only thing that makes me scratch my head is that once up to operating temp and I restart the car, the code goes away and idles/ starts up just fine until it cools down again. But the accel/misfire is still there even if the code is not.

#36 presslab

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Posted 28 December 2012 - 03:00 PM

Your O2 sensor should be toggling back and forth from a low voltage (like 0.1V) to a high voltage (like 0.9V). If it isn't, this means your ECU is not running closed loop for some reason, and can cause lots of problems/misfiring.

Check your O2 voltage back at the ECU, maybe you have a broken wire. Check the voltage from the ground of the O2 sensor (where it screws in) to the ground of the ECU while running. Or maybe you have a different problem and the ECU has run out of adjustment range.

How are you measuring your ground resistance? Is "0.03K Ohm" a typo, as that "K" makes it actually 30 ohms.

#37 86 Wonder Wedge

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Posted 28 December 2012 - 04:14 PM

Yeah, that's a typo.. And I haven't checked the new O2 sensor, but I did a resistance check between the IAC harness and the bundle connector and got 2.3 ohm, and between the bundle and ecu connector, 9.6 ohm. But I could not find and corrosion and no moving of wires yielded any better...

Also, I found something interesting... When i check the resistances for the TPS, on the sensor alone, it starts at 0.62 ohm at idle(0%) from the sensor pin, up to 4.55 ohm at WOT. But when I plug in the connector and backprobe the connector, I start at 0.60 ohm, max at 1.82 at 80% throttle, but back down to 1.62 at WOT. Wtf? Does that have something to do the ECU? But I figured the path of least resistance would still be the same...

#38 naru

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Posted 28 December 2012 - 04:42 PM

Resistance measurements with semiconducters(like the ECU) in the circuit are useless.

Unplug the ECU and measure at the connector.

#39 86 Wonder Wedge

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Posted 28 December 2012 - 09:42 PM

I did and they were the same all the way to the ecu..

On the drive home tonight, I discovered that it won't rev past 5200 no matter what, even in neutral.

So I unplugged the MAF forcing it into open loop, no change.. So I'm leaning toward a worn out injector, or the ecu is failing...

#40 Cougar

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Posted 30 December 2012 - 11:55 AM

When i check the resistances for the TPS, on the sensor alone, it starts at 0.62 ohm at idle(0%) from the sensor pin, up to 4.55 ohm at WOT. But when I plug in the connector and backprobe the connector, I start at 0.60 ohm, max at 1.82 at 80% throttle, but back down to 1.62 at WOT.


The resistance readings that you stated for the throttle sensor seem too low to me. Are you sure those are the correct numbers? Did you leave off a multiplier like 'k' ohm? The resistance to chassis ground would make a large dfference if the numbers you stated were true.

Edited by Cougar, 31 December 2012 - 04:19 PM.


#41 skishop69

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Posted 30 December 2012 - 12:49 PM

You don't normally check resistance on a TPS. I know this sounds odd, but unless you are instructed to, you check the voltage coming out of the TPS. It should start around .4v-.8v and climb to whatever the input voltage is when you reach WOT. Ex: If your input voltage is 5v (as most current systems are), you would see .7v at idle climbing to 4.8 at WOT. As you slowly sweep through the throttle range, pay particular attention to the meter for 'drop outs' which would indicate a dead spot in the TPS. Also, check the resistance of all the incoming grounds to the ECU. I don't have time to right now, but I'll pull the schematics for your car later today. I have to get the roof on my new shed while there's no rain and then do heads on a Ranger. You can't measure resistance on any circuit to the ECU with the circuit connected or with it powered up unless instructed to do so by the FSM. Because it is solid state, you end up measuring parallel resistance of every circuit tied to the one your checking and it won't be what you're expecting to get. I'm still leaning towards ECU since you are developing new symptoms and problems.

#42 86 Wonder Wedge

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Posted 30 December 2012 - 03:49 PM

The FSM dictates that I check the resistance of the TPS, isolated (connector unplugged) verifying that certain resistance are met at certain times (idle, WOT, and the idle switch opens/closes at the correct associated degree of valve opening). It also dictates I check the line resistance at the ECU (connector unplugged) to verify the resistance are withing spec (or matches the readings taken at the TPS). It also has you verify 5V at the TPS plug with KOEO (which it is).

Well, today, she fired up with no code 24, fast idled and let me spin into 6K without bogging (some flat spots above 4K, WOT and feels like fuel cut at spots, but much better). But then when I pull it into neutral coming off the express way, she stalls and upon restart, code 24 is back.

But now I'm starting to feel it's a ground/power distro problem cause sitting at a light before it stalled/code 24, I could hear a VERY light click from behind the dash (maybe radio/clock area?) and the shudder at idle and lower reading on the tach were synchronized like atomic clocks. I couldn't hear it now on the way home (upon several rolling restarts, the code 24 just decides to clear itself :drunk: ) and sitting in the drive way. But now the RR window won't respond and I hear a cyclical clicking coming from that door. Awesome. I'll work on that today (and the rear brakes) and "hopefully" the 1 junkyard within 250 miles (25 from me) has got 2 loyale ECUs left that matches mine AND they aren't shot AND they're open on NYE. Fingers crossed.

#43 Cougar

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Posted 30 December 2012 - 06:56 PM

The code 24 can be caused by an electrical problem with the device or the wiring to it. Either there is a intermittent problem with the wiring to the air valve that is causing the code or a problem with the valve itself. I think there is an intermittent problem with the valve itself and suggest you replace it. Hopefully the troubles will go away then.

Edited by Cougar, 30 December 2012 - 09:26 PM.


#44 skishop69

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Posted 30 December 2012 - 11:34 PM

IIRC... There are a few ECU controlled relays in that area. So, yes. Either grounding or ECU. I wouldn't go spend money on an ECU until you check the grounds to yours, though I suspect you will find them ok or you would be popping random codes besides the 24 when it happens. Shoot me a pm with your email and I'll PDF the schematics and specs tomorrow when I get home from work. I spent 10 hours getting the roof done and I'm fragged. 300sqft of barn roof will do that. Lol

#45 naru

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Posted 31 December 2012 - 10:54 AM

Yeah, that's a typo.. And I haven't checked the new O2 sensor, but I did a resistance check between the IAC harness and the bundle connector and got 2.3 ohm, and between the bundle and ecu connector, 9.6 ohm. But I could not find and corrosion and no moving of wires yielded any better...

Also, I found something interesting... When i check the resistances for the TPS, on the sensor alone, it starts at 0.62 ohm at idle(0%) from the sensor pin, up to 4.55 ohm at WOT. But when I plug in the connector and backprobe the connector, I start at 0.60 ohm, max at 1.82 at 80% throttle, but back down to 1.62 at WOT. Wtf? Does that have something to do the ECU? But I figured the path of least resistance would still be the same...


The reported resistances are waay wrong.

Resistance of the complete potentiometer should be 3500-6500 ohms.
Resistance of the signal line to the appropiate terminal should be less than 1000 ohms w/throttle closed,over 2400 ohms at WOT.

Probably 0.62K ohms = 620 ohms,4.55K ohms = 4550 ohms
Sounds OK to me.

Unplug the ECU.
Try the WOT measurement again at the ECU plug.

Edited by naru, 31 December 2012 - 04:52 PM.
+ K ohms


#46 Cougar

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Posted 31 December 2012 - 04:21 PM

Thanks for the info Naru. Those resistance readings that were stated for the TPS seemed way off to me.

#47 86 Wonder Wedge

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Posted 03 January 2013 - 01:15 PM

Alright. New, hair-pulling info.

After angrily keeping my foot in the firewall when it was doing it normal bogging/power loss above 4K routine, it bucks several times, some relays click, and then takes off like a bat out of hell. Code 24 still exists, but now I've got full power all the way to 7K with no hesitation. The hunting/popping idle still exists, but she hasn't felt this way in months.

After reading the TPS resistances at the ECU plug (with ECU unplugged), I got the same numbers as before (0.62K and 4.55K ohm)

I also checked voltage (with the ECU first unplugged) at pin 45 at got 11.70V KOEO (same at BAT voltage) with code 24 set. When I plug the connector back in, and apply a test light to pin 45, engine running, the code 24 goes away, and the idle picks up, and the code 24 doesn't come back until a few key cycles later or I unplug the connector at the ECU.

I also bit the bullet on a new ECU, same designation and ZERO difference. It was only 50 bucks, so I figured "hey, if the FP driver fails on the original one, I've got a back-up".

I'm doing the voltage before/after 1 min test today now that I've got some time..

#48 Cougar

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Posted 03 January 2013 - 10:38 PM

Maybe you should try replacing the air valve.

#49 naru

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Posted 03 January 2013 - 11:03 PM

Putting a test light on pin 45 grounds the air control valve through the test light.
Seems like you have an ECU grounding issue.
I would backprobe the ECU connector grounds w/a voltmeter between them and battery negative.I think you will see significant voltage on at least one of them.
May explain the other symptoms as well.

#50 86 Wonder Wedge

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Posted 04 January 2013 - 01:51 AM

Putting a test light on pin 45 grounds the air control valve through the test light.
Seems like you have an ECU grounding issue.
I would backprobe the ECU connector grounds w/a voltmeter between them and battery negative.I think you will see significant voltage on at least one of them.
May explain the other symptoms as well.


Yep, which is why I pulled the trigger on a new ECU... while I checked all the ECU grounds from the connectors (with ECU unplugged, of course) they all spec'd out 0.04 ohm (not K ohms this time.. :rolleyes: ) but I didn't do a voltage test.. hmm..

BUT THE GOOD NEWS. I FOUND MY CODE 24 PROBLEM!
I go to try and solve my "no grounding" issue, and I find THIS time, there's no voltage at pin 45 with KOEO. So I pop the hood, unplug the IAC conenctors, find 11.79V at the ECU side of the harness from IGN (W/B wire), 9.6 Ohm on the IAC conenctor across the terminals, >1M ohm to the IAC valve body.

So I plug them back together, find 11.79V going into the valve, 11.79 out (on the IAC side) but 9.1V out on the ECU side at the round bundle conenctor.

So I isolate the "engine harness", run my DMM from the IAC connector to the bundle's appropriate pin, and get 88 ohm. But then I flex the conenctor (since the wiring and conenctor were approx 90 degrees to each other) and then I lose conduction. I move it back, 10 ohm, then 1, then 0.4, back up to 80. I've got a bad wire. HALLELUJAH!

Now, now next question is, when replacing it, do I use another shielded wire? Looking at the FSM, it mentions nothing about the IAC ground wire being shielded (unlike the TPS and O2 sensors), but this has honest to god shielding. It starts about 1.5 inches back from both ends, has black insulation, with fine silver strands, and the factory white insulated 18GA wire beneath it. Luckily, the bad kink is before the shieding, so I wil be soldiering in a new section, but is it that important? And the shielding doesn't ground anywhere, unlike the TPS and O2 sensors... Ideas?




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